The present invention relates to an optical information recording medium of once type such as a CD-R (Compact Disc-Recordable), and more particularly to an optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs.
Generally, a CD-R is known as an optical information recording medium of write-once type which is reproduced by a CD (Compact Disc) drive or a CD-ROM (Compact Disc Read Only Memory) drive.
The optical recording medium such as a CD-R has a basic structure in which a recording layer having an organic dye film is formed on a transparent substrate having a spiral pregroove, a reflecting layer of a metallic film is formed thereon, and further a protective layer of an ultraviolet curing resin is formed thereon, and is configured to record by irradiating a laser beam from the side of the transparent substrate to the recording layer to partly decompose the dye of the recording layer.
This optical information recording medium is expanding its market rapidly because of merits such as compatibility with CDs and a unit cost per bit lower than that of paper, and recording apparatuses, which can write at a recording speed ten times or more higher than an ordinary speed, and corresponding media are being supplied to the market in response to needs for high-speed processing.
Furthermore, it is demanded on the market that a high capacity is provided in correspondence with an increasing amount of data processing every year, and it is assumed that a capacity of 1.3 GB (Giga Bytes) or more is required for an amount of data for image processing or the like.
When the above pits are recorded by means of a laser beam having a wavelength of 780 nm, NA (Numerical Aperture) of 0.45 to 0.50 and a spot diameter of about 1.6 xcexcm employed in the current CD-ROM/-R/-RW drives in order to secure a recording amount of about two times of the currently used ones without changing an outer diameter of conventional optical information recording media of write once type, there are problems as described below.
Specifically, when a tracking pitch is simply changed to have a smaller interval, unwanted signals are taken from an adjacent track when reproducing, namely so-called crosstalk increases, and a clear signal cannot be obtained, resulting in increase of so-called jitter which is the variation in the pit signal at the time of reproduction.
When the recording pits are merely configured to be formed in high density in a linear velocity direction, an effect of heat generated when the pits are formed causes a phenomenon which is called heat interference affecting on the recording state of the next pit, a length of the previously recorded pit and an interval to the next pit become short, so that a position of the next written pit is easily displaced. As a result, a jitter becomes worse. This phenomenon is also seen when recording at a high speed.
It is an object of the present invention to provide an optical information recording medium recordable at a high density two times or more higher than that of currently-used CD-Rs by devising a shape of the pregroove.
The optical information recording medium according to the present invention has a recording layer formed on a transparent substrate having a spiral pregroove formed thereon, wherein a track pitch Tp of the pregroove is 1.0 xcexcmxe2x89xa6Tpxe2x89xa61.2 xcexcm; and an inclination angle Ga of the sidewalls of the pregroove is 30xc2x0xe2x89xa6Gaxe2x89xa670xc2x0.
When the inclination angle Ga of the sidewalls of the pregroove is less than 30xc2x0, a sufficient push-pull voltage amplitude cannot be obtained, so that a wobbling voltage amplitude is small, ATER is accordingly caused, and a trouble is caused in tracking when recording.
When the inclination angle Ga of the sidewalls of the pregroove 201 exceeds 70xc2x0, the entry of the adjacent track into an edge of a spot increases an amount of crosstalk, leading to worsening of jitter because a portion having a phase difference larger than that when the inclination is not larger than 70xc2x0 enters into the spot.
It is desirable that a half-width Gw of the pregroove is in a range of 0.25 xcexcmxe2x89xa6Gwxe2x89xa60.50 xcexcm. The half value width Gw of the pregroove is a width at a position with a half of the depth Gd of the pregroove. When the half value width Gw of the pregroove exceeds 0.50 xcexcm, a pit width Pw increases when recording, and an effect of crosstalk increases, and when it is less than 0.25 xcexcm, it is necessary to increase the laser power required for recording, and sufficient reproduction modulation cannot be obtained, resulting in an increase of a block error rate which is a reproduction signal error value.
It is preferable that a depth Gd of the pregroove is determined to 100 nmxe2x89xa6Gdxe2x89xa6300 nm. When the depth Gd of the pregroove is less than 100 nm, tracking becomes difficult, and when the depth Gd of the groove exceeds 300 nm, injection molding of the pregroove becomes difficult.
A width Lw of the land formed between the pregrooves is preferably determined to Lwxe2x89xa70.6 xcexcm. The width Lw of the pregroove is defined by a difference Td-Gw between a track pitch Td and the half value width Gw of the pregroove, and when the width Lw of the land is less than 0.6 xcexcm, crosstalk increases, and jitter becomes large.
A wobbling amplitude Wamp of the pregroove is preferably determined to a range of 20 nmxe2x89xa6Wampxe2x89xa645 nm. In this type of optical information recording medium, the pregroove is wobbling, and it is configured to record information by detecting an absolute time according to the wobbling signal obtained from the wobbling shape, but when the wobbling amplitude Wamp of the pregroove is less than 20 nm, the wobbling signal becomes small and tracking is difficult when recording, and when the wobbling amplitude Wamp of the pregroove exceeds 45 nm, the wobbling signal has a problem of crosstalk, and tracking becomes difficult when recording.